1. Field of the Invention
The invention pertains generally to the formation of contoured surfaces requiring structural backup, and more particularly to conductive contoured surfaces such as required for radar reflectors.
2. Description of the Prior Art
Radar reflectors have been fabricated in various ways in the prior art. A typical reflector comprises a contoured concave reflective surface of sheet metal or a conductive mesh having dimensional parameters for the frequency or band-to-frequencies concerned causing it to perform substantially as a continuous conductive sheet.
The typical radar reflector or "dish" is rotatably mounted and is exposed to wind and other environmental forces. The accuracy and stability of the contoured reflector surface must meet close tolerances from the time of manufacture and throughout extended service. Often a rigid sheet with complex back support and cross-bracing has been employed, the manuacture thereof requiring complex and costly tooling.
Other approaches to the construction of radar reflectors in particular, include the "lay-up" of a structural plastic reflector surface over a conductive mesh spread over a convex mandril which provides a mold for the desired concave reflector shape. To obtain the desired rigidity over the long term, various reinforcing members must be built directly into the plastic lay-up , and a metallic backup arrangement usually a metallic structural network assembled to provide a rigid backup and shape-holding function, is required. This extra backup structure usually also provides the pedestal interface by means of which the reflector is rotated in at least one plane.
In addition to cost, the matter of weight is also an important consideration since rotating radar reflectors are often placed on towers, masts or other structures, those being required to be correspondingly heavy if the reflector structure itself is heavy.
In accordance with the foregoing it will be understood that light, strong and inexpensively manufactured radar reflector structures are of great technical and economic importance.
In the search for radar reflector constructions meeting the aforementioned objectives of strength and low-cost, etc., a so-called "egg-crate" structure has evolved in the prior art. In that prior art, a plurality of horizontal and vertical ribs are notched together. The desired reflecting surface contour is cut into these ribs so that their edge is adjacent to the reflecting surface, each provides a shape appropriate for the location of each rib within the structure. The resulting structure is both a template for forming the mesh reflector surface and is also the supporting structure for the reflector in operation.
Obviously, the prior art horizontal and vertical ribs form square or rectangular spaces backing up the actual reflector mesh surface, however additional structural bracing and support is required in order to prevent these square or rectangular spaces from deforming into parallelograms. That deformation could occur during fabrication or in operation absent a substantial amount of additional bracing and over structure. Still further, the periphery of a reflector fabricated in this manner is generally rectangular in projected outline, whereas the primary feed pattern of a microwave horn associated therewith for illuminating the reflector tends to project equal-power contours onto the reflector which are of themselves elliptical. Accordingly, a mismatch develops and is reflected into the illuminating horn and its associated microwave components, adversely affecting the efficiency of operation. Moreover, spill-over losses and increased side lobe levels in the transmitted (or received) overall antenna pattern result.
The manner in which the invention overcomes the aforementioned prior art difficulties will be understood as this description proceeds.